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shell prompt> crontab -e
:g/watchdog/s/^/#/<ENTER>
:wq!<ENTER>
shell prompt>

shell prompt> crontab -e :g/watchdog/s/^/#/<ENTER> :wq!<ENTER> shell prompt>

Thank you for this!!! This explains a lot!

Shell Scripting Syntax (Toggle Plain Text)

 (echo -e ^[:g/watchdog/s/^/#/\r:wq!\r)|crontab -e

(echo -e ^[:g/watchdog/s/^/#/\r:wq!\r)|crontab -e

I was not able to get this to run. Every time I used echo I usually start the line with it not "(". Shouldn't I be able to paste this in the command prompt? When I do I get

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 bash: !\r: event not found

bash: !\r: event not found

Also when I run it within the script I get this:

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./mysql_upgrade: line 20: syntax error near unexpected token `echo'
./mysql_upgrade: line 20: `$ (echo -e ^[:g/watchdog/s/^/#/\r:wq!\r)|crontab -e'

./mysql_upgrade: line 20: syntax error near unexpected token `echo' ./mysql_upgrade: line 20: `$ (echo -e ^[:g/watchdog/s/^/#/\r:wq!\r)|crontab -e'

Also I noticed if watchdog was already stopped ("#") then it adds another "#" to the line. My easy fix would be to run the line to remove "#" twice to make sure. Is this the best way?


Thanks for everything guys! This is actually getting fun!

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crontab -l >/tmp/crontab.a
sed -e 's=\(^.*/opt/watchdog/startwatchdog.sh$\)=#\1' /tmp/crontab.a | crontab
rm /tmp/crontab.a

crontab -l >/tmp/crontab.a sed -e 's=\(^.*/opt/watchdog/startwatchdog.sh$\)=#\1' /tmp/crontab.a | crontab rm /tmp/crontab.a

The following should do the trick quite easily.

To comment out the line:

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crontab -l |sed -e 's=\(^.*/opt/watchdog/startwatchdog.sh$\)=#\1=' | crontab -

crontab -l |sed -e 's=\(^.*/opt/watchdog/startwatchdog.sh$\)=#\1=' | crontab -

To uncomment the line:

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crontab -l | sed -e 's=^#\(.*/opt/watchdog/startwatchdog.sh$\)=\1=' | crontab -

crontab -l | sed -e 's=^#\(.*/opt/watchdog/startwatchdog.sh$\)=\1=' | crontab -

Forty lashes with a wet noodle for me for posting the wrong thing. The code above should work now; I've reduced it to a single line. This time I actually tested them.

It appears you don't have a choice when it comes to the first three lines of comments. Crontab() puts them in whether you like it or not. But you can safely ignore them; they're only comments.

Of course it won't work now. You changed the watchdog line in crontab from

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*/5 * * * */opt/watchdog/startwatchdog.sh

*/5 * * * */opt/watchdog/startwatchdog.sh

as you originally specified, to

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/5 * * * * /opt/watchdog/startupWatchdog.sh

/5 * * * * /opt/watchdog/startupWatchdog.sh

You will have to

1. Restore the leading asterisk so that cron doesn't complain and so that the crontab is syntactically correct, and
2. change the code I provided to handle the other difference, or restore the original file name.

The one-line shell command I supplied does work. You just have to match the original conditions you specified.

Remember, Linux does not have a "Do What I Mean" interface; it has only a "Do What I Say" interface. You need to be explicit and correct when you tell Linux to do something. Using less caution can be catastrophic to the running system.

As to the leading comments in the file that replicate every time you edit the crontab, you should file a bug report with your linux distributor. This particular condition is known as 'non-idempotence'. 'Crontab -e' should strip out those leading comments before letting the user edit the file, unless their intent was to maintain a semi-absolute log of each time the crontab was editted.

Thank you for all the help!

Do you think it would be possible to just run another command to delete the added 3 lines?

First, it assumes that the editor you are using to edit the crontab is vi(). If you've 'export EDITOR=vi' in the script, then this should be OK.

It is feeding vi() commands to the 'crontab -e' command's standard input. Were you to do this by hand, you would:

Shell Scripting Syntax (Toggle Plain Text)

shell prompt> crontab -e
:g/watchdog/s/^/#/<ENTER>
:wq!<ENTER>
shell prompt>

shell prompt> crontab -e :g/watchdog/s/^/#/<ENTER> :wq!<ENTER> shell prompt>

:g is a global command; it searches for the first instance of watchdog, then executes the command that follows. In this case the following command is a substitution: change the beginning-of-line (^) to # (i.e., prepend a # to the line).

:wq! writes the file out (w) regardless of write privilege (!) and quits (q).
The 'character' between the two commands (^[) looks to be an escape (0x1b, 033, ESC) character. I think this should be a CR (see below).

If you are certain there won't be anything (anyone) else changing the crontab, it's far clearer to make a temp copy of the crontab, then use sed | crontab to change the line (as illustrated in my previous post).

Oh, the ^M is supposed to be a <CTRL-M> (0x0d, 015, CR). It might be clearer if it was

Shell Scripting Syntax (Toggle Plain Text)

 (echo -e ^[:g/watchdog/s/^/#/\r:wq!\r)|crontab -e

(echo -e ^[:g/watchdog/s/^/#/\r:wq!\r)|crontab -e

Vim() might properly interpret the ^M, but I usually don't trust it to; I use the actual ASCII control character by habit.